The invention relates to the use of pulsating electromagnetic signals for stimulating chondrogenesis. In particular, it relates to the use of FGF (fibroblast growth factor) in combination with pulsating electromagnetic signals for stimulating cartilage and chondrogenesis.
It is known that under physiological conditions healthy cartilage of the joints is subject to strain and that this may lead to attrition of cartilage along with destruction of the cartilage surface. Also inactivity and changes in the synovia caused by infection may result in destruction of cartilage.
Cartilage is a structural tissue consisting of chondrocytes, rich in water, and an intercellular substance. 60 to 80% of the extracellular matrix of cartilage consists of water. The intercellular substance is composed of basic substances (proteoglycans and glucoproteins) as well as filaments (collagen). Proteoglycans, glucoproteins and collagen are manufactured by chondrocytes. Collagen forms a texture in which proteoglycans and glucoproteins are embedded and held in place.
There are a number of different kinds of collagen. Collagen molecules of types I, II, III, V, and VI have similar molecular structures. Collagen molecules of types IX, XII, and XIV contain a number of triple helix domains that are interrupted by non-collagen domains. Also there are differences among the various kinds of collagen molecules. Type V collagen molecules have a low alanin content, but a high content in basic amino acids. In addition, they form tetramers. Type VIII is a strong protease. Type IX is found on the surface of collagen type II. Type XI collagen molecules are short triple helices with very long globular extensions. Type VII Collagen molecules have an N-terminal domain region with three fingers similar to collagen types XII and XIV.
Proteoglycans form hydrated gels through which nutrients reach the chondrocytes by diffusion. Proteoglycans are macromolecules, which consist of a protein nucleus to which a number of glycosamine glycan chains are bound. Components of glycose amine glycans comprise disaccharides with negatively charged sulfate and carboxyl groups, which determine the charge density of the extracellular cartilage matrix.
These negative charges are neutralised by sodium ions of the extracellular fluids. For this reason, a considerable amount of sodium is contained in cartilage, giving rise to high osmotic pressure, attracting water, wherefore 80% of cartilage consists of water.
Under pressure, cartilage is compressed, the water is displaced taking with it the mobile sodium ions, while the negatively charged carboxyl and sulfate ions of the proteoglycan are left behind. This process creates an electrical current, since non-neutralized negative charges are present in the cartilage. According to the Donnan effect, the negative charges determine the concentration of gegenions. The negative charges and the electrical current generate an electrical charge. When the pressure is released, sodium ions and water are once more attracted and the cartilage expands once more to its original volume.
Via this mechanism, chondrocytes are stimulated to synthesize additional matrix. Biosynthetic productivity of the chondrocytes depends on extracellular osmolarity, wherefore it may be assumed that mechanical and physio-chemical conditions are important prerequisites for transmission of signals in conjunction with the pressure applied.
Cartilage flow potentials may be altered by reduction of proteoglycan content, for example, by enzymatic decomposition of chondrocytes. Changes in the extracellular matrix therefore must also lead to changes in electrical phenomena so that the chondrocyte receives altered signals, which influence synthesis productivity.
In osteoarthritis, wear and tear of the cartilage occurs so that the matrix is lost. The cartilage can no longer perform its normal functions due to loss of matrix components, since the amount of proteoglycans present is less. In addition, it has been found in the laboratory that afflicted cartilage and other neighboring tissue of the joint swells, and therefore less current can flow.
A so-called magnetic field therapy is known which is applied to non-healing bone fractures. In magnetic field therapy, sinus shaped, continuous alternating current is applied having a frequency of approximately 44 to 77 Hz and field strength of 2 G.
FGF is known to be a growth stimulant for fibroblasts. FGF is subdivided into basic FGF (bFGF) and acidic FGF (aFGF). Basic FGF is present in cartilage and bones and is involved in the development and growth of cartilage. Various forms of bFGF have been reported found in the nucleus and cytoplasm as well as in the extracellular matrix of cells. Application of bFGF induces chondrocyte to multiply and synthesize extracellular matrix (see Cuevas, P., Burgos, J., and Baird, A., Basic Fibroblast Growth Factor (FGF) Promotes In Vivo Cartilage Repair, Biochem. Biophys. Res. Commun., 31, 611, 1988). Also, it was found that injection of aFGF (1 xcexcg/d) at the site of bone fracture increases chondrogenesis and osteogenesis (see Jingushi, S., Heydemann, A., Kana, S. K., Macey, L. R., and Bolander, M. E., Acidic fibroblast growth factor (aFGF) injection stimulates cartilage enlargement and inhibits cartilage gene expression in rat fracture healing, J. Orthop. Res., 8, 364, 1990).